The present invention relates to a method of building a tobacco stream on an air-permeable conveyor and to an apparatus which can be used in the distributor of a cigarette rod making machine for the making of a tobacco stream which is to be converted into, or which can constitute, a tobacco filler, i.e., the tobacco-containing constituent of a cigarette rod.
It is known to build a tobacco stream at one side of an air-permeable conveyor the other side of which is adjacent to a suction chamber in order to attract the particles of tobacco to the conveyor while such particles are in the process of forming a growing tobacco stream as well as to attract the fully grown stream during transport toward the trimming station or directly to the wrapping station of the rod making machine. Tobacco particles are propelled by streams of compressed air to travel across an elongated channel which is defined by the conveyor and two spaced-apart sidewalls and is adjacent to the one side of the conveyor. In many instances, the tobacco channel has a rectangular cross-sectional outline and the means for supplying tobacco can constitute an arcuate guide wall the concave side of which serves as a support for the tobacco stream which is caused to advance toward and into the channel. The directions of air streams which advance the particles of tobacco along the guide wall are such that the particles which leave the guide wall travel across the channel and impinge upon the one side of the conveyor. Reference may be had to commonly owned U.S. Pat. No. 4,175,570 granted Nov. 27, 1979 to Uwe Heitmann. A drawback of presently known apparatus which build a continuous tobacco stream in the aforeoutlined manner is that the conditions in the channel are unpredictable. Thus, the air streams are likely to form eddy currents and/or other stray currents which prevent predictable propagation of tobacco particles from the guide wall toward the conveyor in such a way that the latter can accumulate a homogeneous tobacco stream. It has been found that the density of the thus formed tobacco stream is not always uniform. For example, the density of a freshly formed tobacco stream is less pronounced along the marginal portions of the conveyor (adjacent to the two sidewalls) than along the central portion. This affects the quality of the filler which is obtained when the surplus of tobacco particles is removed from the fully grown stream. The inability of conventional apparatus to form a homogeneous tobacco stream with a requisite degree of predictability and for extended periods of time is also attributable to the fact that the channel must receive relatively large quantities of air in order to ensure the admission of requisite quantities of tobacco particles and that the evacuation of surplus air (namely, of that percentage of air which cannot be evacuated through the air-permeable conveyor) presents many problems.